The present invention relates to electrical discharge machining (EDM) systems and methods, and more particularly to control systems for such systems and methods.
Electrical discharge machining (EDM), also referred to as spark machining, spark eroding, burning, die sinking, wire burning, or wire erosion, is a manufacturing process whereby a desired shape is obtained using electrical discharges. Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes. One of the electrodes is the tool, or simply the electrode, and the other of the electrodes is the workpiece.
EDM systems and methods, and control systems for such systems and methods, are well known to those skilled in the art. An example of a prior art EDM system is illustrated in FIG. 1. The prior art system 10 includes an electrode 12, a spindle support 14, and a workpiece holder 16. The electrode 12 moves along a linear axis Z′. The spindle support 14 moves a spindle, holding the electrode, along three linear axes X, Y, and the Z. The workpiece holder 16 moves about two rotational axes A and B.
The system 10 further includes an EDM controller 18 and a machine axis position controller 20. Process recipes are stored in a memory 22. The movement of the electrode 12 along the Z′ axis is controlled by the EDM controller 18. The movement of the spindle support 14 and the workpiece support 16 along and about the X, Y, Z, A, and B axes is controlled by the machine axes controller 20. The target Z′ position is determined based on a measured gap voltage between the expendable electrode 12 and the workpiece. The program flowchart for the described system is illustrated in FIG. 2.
The described EDM system has proven to be highly effective for machining straight through-going holes. Problems are presented, however, when the approach is applied to the drilling and/or milling of three-dimensional shapes. The machine axes controller 20 presents the workpiece by way of rotary axes A and B and controls the tool position by moving the spindle support along axes X, Y, and Z. The EDM controller 18 positions the electrode 12 on the Z′ axis based on a gap voltage and calculated parameters and applies power supply settings based on a single recipe for a given hole.
However, the described EDM system has at least three drawbacks. First, after a burn is initiated, the process recipe cannot be changed without stopping the programmed tool path. Second, while the burn runs as a closed loop process for the Z′ axis, the burn runs as an open loop process for the X, Y, Z, A, and B axes. Consequently, movement along or about these axes is unaffected by anything happening during the burn. Third, only the EDM controller 18 is responsive to the gap voltage and other burn parameters. All of these drawbacks negatively impact dimensional accuracy, hole surface quality, and cycle time.